The present invention relates to an electrophotosensitive material which is used for image forming apparatuses utilizing an electrophotography, such as electrostatic copying machine, laser beam printer, etc.
The electrophotography such as Carlson process includes a step of uniformly charging the surface of an electrophotosensitive material by a corona discharge; an exposure step of exposing the surface of the charged electrophotosensitive material to form an electrostatic latent image on the surface of the electrophotosensitive material; a developing step of bringing the formed electrostatic latent image into contact with a developer to visualize the electrostatic latent image due to a toner contained in the developer to form a toner image; a transferring step of transferring the toner image on a paper; a fixing step of fixing the transferred toner image; and a cleaning step of removing the toner remained on the photosensitive material.
As the electrophotosensitive material to be used for the above electrophotography, there have recently been suggested various organic photoconductors using an organic photoconductive compound having little toxicity in place of an inorganic photoconductive material (e.g. selenium, cadmium sulfide, etc.) whose handling is difficult because if it's toxicity. Such an organic photoconductor has an advantage such as good processability, easy manufacturing and great deal of freedom for design of performance.
As the organic photoconductor, a distributed function photosensitive layer containing an electric charge generating layer which generates an electric charge by light irradiation, and an electric charge transferring layer which transfer the generated electric charge is exclusively used.
A lot of studies about a binding resin which contains the above electric charge generating material and electron transferring material (consisting of hole transferring material and/or electron transferring material) and constitutes a photosensitive layer have been made so as to increase a mechanical strength (e.g. wear resistance, scratch resistance, etc.) of the photosensitive layer to prolong the life of the photoconductor. Particularly, polycarbonate resins (e.g. bisphenol A type, C type, Z type, fluorine-containing type, biphenyl copolymer type, etc.) have widely been utilized (Japanese Laid-Open Patent Publication Nos. 60-172045, 60-192950, 61-62039, 63-148263, 63-273064, 5-80548 and 5-88396).
In addition, it has also been known that the mechanical strength of the photosensitive layer is improved by increasing the molecular weight of the above polycarbonate resin (Japanese Laid-Open Patent Publication Nos. 5-113671 and 5-158249).
The mechanical strength of the photosensitive layer is improved by using the above-described polycarbonate resin as the binding resin, but the degree of the improvement is insufficient. In addition, the polycarbonate resin is inferior in compatibility with electric charge transferring material and despersion properties and, therefore, characteristics thereof can not be sufficiently utilized even if a material having excellent hole transferring characteristics is used. Accordingly, the sensitivity becomes inferior.
Furthermore, regarding a single-layer type photoconductor containing an electric charge transferring material and an electric charge generating material in a single layer, when using the polycarbonate resin as the binding resin in the photosensitive layer, the photosensitive layer is peeled off from a conductive substrate while using because the polycarbonate resin is inferior in adhesion to the conductive substrate such as aluminum, etc.